Many information authentication media, such as passports and ID (identification) cards, use facial images to enable visual information authentication. For example, conventionally, in a passport, a piece of photographic paper, with a facial image printed thereon, is stuck to the booklet body of the passport. However, there is a risk that such a passport is falsified by replacement of the printed image with another one.
For this reason, recent trends are toward digitizing facial image and reproducing the facial image on a booklet body. Methods for reproducing such an image now being considered include a thermal transfer recording method using a transfer ribbon, such as a resin-mold melt type transfer ribbon or a wax melt type transfer ribbon, in which a sublimable, i.e. thermally transferable, dye or pigment is dispersed, or an electrophotographic method.
Methods for reproducing an image on a passport include, besides the above mentioned ones, a recording method using an ink jet printer (PTL 1), a laser printing/recording method using a carbon dioxide gas laser or YAG (yttrium aluminum garnet) laser or using a heat-sensitive color-producing reagent (PTL 2), or a laser engraving printing/recording method with which data can also be printed/recorded in a depth direction of a base using carbon (C) present in the base (PTL 3).
Further, known image displays equipped with this type of recognition data include a display in which an image pattern formed on the basis of image data is provided on a card base made such as of polyvinyl chloride. Also, there is a known display which is provided, in addition to the above image pattern, with an OVD (optically variable device) image represented by an image obtained by using a hologram or a diffraction grating, or by using an optical thin film that makes use of multi-layer interference. It should be noted that optical thin films can exhibit an effect such as color shifting by virtue of their optical design.
Hologram or diffraction grating structures are each used as an anti-counterfeiting means by being stuck onto various objects. The various objects include various cards, such as credit cards, cash cards, membership cards, company ID cards, prepaid cards and driving licenses, various paper credits, such as money coupons, gift tickets and stock certificates, various business forms, such as application forms, bill-payment receipts and duplicate slips, and various booklets, such as passports, passbooks, pension books, generally used pocketbooks and books, and panels, such as displays.
The anti-counterfeiting media on which such OVD images are formed can be easily forged because these media can be visually recognized. As a measure against this, there has been recently proposed an anti-counterfeiting technique using a covert function for determining authenticity by making use of a polymer liquid crystal material. The covert function normally disables visual confirmation of a latent image but enables visual confirmation of the latent image only when a filter is held over the latent image (PTL 4).
As a method for forming a desired image having the covert function mentioned above, PTL 5 proposes an anti-counterfeiting medium in which a desired birefringent pattern is formed. The birefringent pattern can be formed by patterning an ink composition that contains a liquid crystal compound on an oriented layer by means of an inkjet method.
In PTL 6, color component materials used for coloring layers producing black or other colors can also be used for a coloring layer of a recording medium. PTL 6 proposes that a method of using a heat-sensitive microcapsule is a scheme effective for producing color with low energy.
PTL 7 shows, as an example, another color component material composed of a compound and a photopolymer that enable laser marking.
The material disclosed as an example in PTL 7 is used as a material that contains at least one of: a plastic material that is modified by laser irradiation; an inorganic material that accelerates modification; a plastic material that contains an organic material; and an inorganic material that absorbs irradiated laser and generates heat.